One of the problems encountered in systems employing hydrocarbon fuels is the build up over time of thermal oxide derived varnish-like lacquer deposits on the surfaces of combustion chambers and components of the fuel distribution network. One of the commonly used methods for rating an engine lubricant involves examination of a test piston which has been subjected to many hours of operation in a running engine. Lubricant efficacy can be measured, in part, by measuring the amount of lacquer and carbon which has been deposited on the piston surface (lands) and in the ring grooves. Currently, this evaluation procedure is done manually, using human judgement to classify the deposit color and coverage.
Currently lacquer deposits are categorized according to six classifications based on color: (1) clean (shiny aluminum, no deposits); (2) very light amber lacquer; (3) light amber lacquer; (4) amber lacquer; (5) dark brown lacquer; and (6) black lacquer. Each lacquer classification is slightly darker than the previous one, beginning with no lacquer deposit (clean) and ending with black (class 6 above). Under standards issued by the Coordinated Research Council (CRC) rating specification any lacquer deposit appearing to have a color value falling between two classes is given the higher class categorization. One of the difficulties with current inspection techniques is the use of subjective judgment on the part of the operator who classifies the lacquer deposit based on his individual perception of the "best match" to the color standard.
From the above discussion, it is clear that the prior art lacks an objective, precise and repeatable evaluation technique for evaluating lacquer and carbon deposits on surfaces of internal combustion engine. A method and apparatus of the present invention, discussed in more detail below, provides an efficient and effective inspection technique overcoming the difficulties of the prior art.